Supplementation with a leucine-enriched essential amino acid mixture during training may protect untrained men from muscle damage and boost muscle recovery, says a new study from Japan.

Eight days of supplementation with the leucine-enriched essential amino acid (LEAA) mixture were associated with significant reductions in creatine phosphokinase (CPK), a marker of exercise-induced muscle damage, according to scientists from Tsukuba University of Technology, University of Tsukuba, Hokkaido Nippon-Ham Fighters, and Ajinomoto Co.

On the other hand, no changes were observed for maximal isometric strength in the untrained men participating in the study.

“Our results showed that the 3.6 g dose (21 mg leucine per body weight) of orally administered LEAA supplement was efficiently absorbed and was sufficient to elevate serum levels of EAA and leucine for several hours after ingestion,” ​they wrote in the Journal of Physical Therapy Science​​​.​

Study details​

The researchers recruited 10 untrained men with an average age of 23 to participate in their randomized, double-blind cross-over study. The men were randomly assigned to consume either 3.6 grams of the LEAA supplement (containing 1.44 grams of leucine, 0.6 g of lysine, 0.4 g of valine, 0.39 g of isoleucine, 0.34 g of threonine, 0.24 g of phenylalanine, 0.12 g of methionine, 0.06 g of histidine, and 0.03 g of tryptophan) three time per day (so a total daily dose of 10.8 g) or a maltitol placebo three times per day for eight days. These was followed by a three-week washout period after which the men crossed over to the other intervention group for a further eight days.

Results showed that serum CPK activity increased in both groups, but the increase was significantly lower in the LEAA group, suggesting less muscle damage during LEAA supplementation. However, there were no significant differences between the groups for myoglobin concentration or self-reported muscle soreness during the study.

Convincing? ​

Commenting independently on the study’s findings, Dr Ralf Jaeger, Managing Member of Increnovo LLC, told us that the results of this study looked at in isolation would not convince him that BCAAs have physiologically meaningful benefits.

However, they do fit with a wider body of studies using BCAAs that have illustrated improved time course changes after damage and supplementation. There are, however, also studies that show little effect of BCAAs on recovery, he added.

“The design is right (single limb muscle damaging exercise, resulting is 40% reduced performance and increase in markers of muscle damage, showing the exercise was challenging enough, looking at performance, subjective and objective measures), however, using a relative ratio for this type of study design is very uncharacteristic and was likely heavily underpowered,”​ said Dr Jaeger.

Training status is a critical variable, he added. “These people were untrained thus their damage response was likely amplified vs. a trained population. Eccentric damage of the upper arm (biceps) is brutal and invokes uncharacteristic swelling and damage. This could help explain why after 5 days values were still elevated,”​ said Dr Jaeger.

“I personally would like to see matching outcomes of the different measurements (performance, subjective and objective measures), showing significant improvements during the first three days post muscle damaging exercise,”​ he added.